1. Field of the Invention
The present invention relates to organic polymers suitable for use in anti-reflective coatings on semiconductor devices, and methods for preparing them. More specifically, the polymers of the present invention can be used to form a layer which prevents the reflection of light from lower layers coated on a semiconductor chip when photolithography processes using 193 nm (ArF) wavelengths are employed during the manufacture of 64 M, 256 M, 1 G, 4 G and 16 G DRAM semiconductor devices. Anti-reflective coatings comprising polymers of the present invention also eliminate the standing wave effect when an ArF beam is used, and reflection/diffraction caused by changes in the thickness of the photoresist layer itself. The present invention also relates to anti-reflective compositions containing these polymers and anti-reflective coatings formed from these compositions, as well as preparation methods therefor.
2. Description of the Prior Art
In photolithography processes for forming ultrafine-patterns during the manufacture of semiconductors, it is unavoidable to have reflective notching of the standing wave of the exposing radiation. This effect is due to the spectroscopic properties of the lower layers coated on the semiconductor wafer, changes in the photoresist layer and variations in the critical dimension (CD) due to diffracted and reflected light from the lower layer. Therefore, it has been suggested that a layer, called an anti-reflective coating, be introduced into the semiconductor device to prevent the reflection of light from the lower layers. This anti-reflective coating usually comprises an organic material that absorbs light in the wavelength range of the light beam source used in the lithography process.
Anti-reflective coatings are categorized into inorganic and organic anti-reflective coatings depending on the coating materials used, or into light-absorbing and light-interfering coatings depending on the mechanism.
An inorganic anti-reflective coating is used mainly in the process of ultrafine-pattern formation using i-line radiation with a wavelength of 365 nm. TiN and amorphous carbon have been widely used in light-absorbing coatings, and SiON has been used in light-interfering coatings.
Inorganic SiON has been used for anti-reflective coatings in ultrafine-pattern formation processes using a KrF beam. A recent trend has been to try to use organic compounds in an anti-reflective coating. Based on knowledge to date, the following are prerequisites for an adequate organic anti-reflective coating:
First, during the pattern formation process, the photoresist must not be peeled from the substrate by dissolving in the solvent used in the organic anti-reflective coating. For this reason, the organic anti-reflective coating needs to be designed to form a cross-linked structure, and must not produce chemicals as a by-product.
Second, acid or amine compounds must not migrate in or out of the anti-reflective coating. This is because there is a tendency for undercutting at the lower side of the pattern if an acid migrates, and for footing if a base such as an amine migrates.
Third, the anti-reflective coating must have a faster etching speed compared to the photoresist layer so that the etching process can be performed efficiently by utilizing the photoresist layer as a mask.
Fourth, the anti-reflective coating must function with a minimal thickness.
Up to now, suitable anti-reflective coatings have not been developed for use in processes for forming an ultrafine-pattern using an ArF beam. Furthermore, since there is no known inorganic anti-reflective coating that controls the interference from a 193 nm light source, the use of organic chemicals in anti-reflective coatings is currently being studied.
Therefore, it is desirable to use and develop organic anti-reflective coatings that absorb light strongly at specific wavelengths to prevent the standing wave effect and light reflection in lithography processes, and to eliminate the rear diffraction and reflected light from the lower layers.
The present invention provides novel chemical compounds suitable for use in anti-reflective coatings in photolithography processes for forming ultrafine-patterns using 193 nm (ArF) and 248 nm (KrF) light beams in the manufacture of semiconductor devices.
The present invention further provides preparation methods for chemical compounds to be used in anti-reflective coatings.
The present invention also provides anti-reflective coating compositions containing the above-mentioned compounds and preparation methods thereof. The present invention also provides anti-reflective coatings formed by using the above-mentioned anti-reflective composition, and methods for the formation thereof.
The polymers of the present invention comprise a monomer with a phenyl group and an amide linkage having high absorbance at 193 nm, so that the polymer resin absorbs 193 nm wavelength light. A cross-linking mechanism using a ring opening reaction is introduced into preferred polymer resins of the invention by adding another monomer having an epoxy structure, so that a cross-linking reaction takes place when coatings of the polymer resins are xe2x80x9chard bakedxe2x80x9d, i.e., heated at a temperature of 100-300xc2x0 C. for 10-1,000 seconds. Accordingly, a great improvement can be effected in the formation, tightness and dissolution properties of the anti-reflective coatings using polymers of the present invention. Particularly, maximal cross-linking reaction efficiency and storage stability are realized by the present invention. The anti-reflective coating resins of the present invention have superior solubility in all hydrocarbon solvents, in order to form a coating composition, yet are of such high solvent resistance after hard baking that they are not dissolved in any solvent at all. These advantages allow the resins to be coated without any problem to form an anti-reflective coating which prevents undercutting and footing problems when images are formed on the overlying photosensitive layer. Furthermore, coatings made of the acrylate polymers of the invention are higher in etch rate than the photosensitive film coatings, thereby improving the etch selection ratio therebetween.
Preferred copolymer resins according to the present invention are represented by the following general formula 1: 
wherein, Ra, Rb, Rc and Rd each represents hydrogen or methyl; R1 represents hydrogen, hydroxy, a substituted or non-substituted straight or branched C1-C5 alkyl, cycloalkyl, alkoxyalkyl or cycloalkoxyalkyl; w, x, y and z each represents mole fraction of 0.01-0.99; and n1 and n2 each represents an integer of 1 to 4.
and by the following general formula 2: 
wherein, Ra, Rb, and Rc each represents hydrogen or methyl; R1 represents hydrogen, hydroxy, a substituted or non-substituted straight or branched C1-C5 alkyl, cycloalkyl, alkoxyalkyl or cycloalkoxyalkyl; x, y and z each represents mole fraction of 0.01-0.99; and n represents an integer of 1 to 4.
The polymer resins of the present invention are particularity suitable for use in organic anti-reflective coatings since they comprise a monomer having a phenyl group and amide linkage having excellent absorbency of 193 nm wavelenth radiation. Preferred monomers comprise a p-tosylalkylacrylamide-type monomer of the following chemical formula 3: 
wherein R is hydrogen or methyl.
The polymers represented by general formula 1 can be prepared in accordance with the reaction equation 1 set forth below, wherein a p-tosylalkylacrylamide-type monomer, an hydroxyalkylacrylate-type monomer, a methylacrylate-type monomer and a glycidylacrylate-type monomer are polymerized with the aid of an initiator in a solvent. Each of the monomers has a mole fraction ranging from 0.01 to 0.99. 
wherein, Ra, Rb, Rc and Rd each represents hydrogen or methyl; R1 represents hydrogen, hydroxy, a substituted or non-substituted straight or branched C1-C5 alkyl, cycloalkyl, alkoxyalkyl or cycloalkoxyalkyl; and n1 and n2 each represents an integer of 1 to 4.
The polymers represented by general formula 2 above can be prepared in accordance with the reaction equation 2 set forth below, wherein a p-tosylalkylacrylamide-type monomer, an hydroxyalkylacrylate-type monomer and a methylacrylate-type monomer are polymerized with the aid of an initiator in a solvent. Each of the monomers has a mole fraction ranging from 0.01 to 0.99. 
wherein, Ra, Rb, and Rc each represents hydrogen or methyl; R1 represents hydrogen, hydroxy, a substituted or non-substituted straight or branched C1-C5 alkyl, cycloalkyl, alkoxyalkyl or cycloalkoxyalkyl; and n represents an integer of 1 to 4.
Conventional radical initiators, preferably 2,2-azobisisobutyronitrile (AIBN), acetylperoxide, laurylperoxide or t-butylperoxide, may be used for initiating the polymerization reaction forming the polymers of general formulas 1 and 2. Also, conventional solvents may be used for the polymerization, preferably tetrahydrofuran, toluene, benzene, methylethylketone or dioxane. Preferably, the polymerization for the polymers of the general formulas 1 and 2 is carried out at 50-80xc2x0 C.
Semiconductor devices of the present invention may be prepared as described below. The copolymer of general formula 1 or formula 2 may be dissolved in a suitable solvent alone, or with a cross-linker additive selected from acrolein, diethylacetal and melamine-type cross linkers, at an amount of 0.1 to 30 % by weight. The solution is filtered and coated on a wafer and then hard-baked to form a cross-linked anti-reflective coating. Semiconductor devices can then be fabricated therefrom in the conventional manner.
Conventionl organic solvents may be used in preparing the anti-reflective coating composition, with preference given to ethyl 3-ethoxypropionate, methyl 3-methoxy propionate, cyclohexanone or propyleneglycol methyletheracetate. The solvent is preferably used at an amount of 200 to 5000% by weight based on the weight of the anti-reflective coating resin copolymer used.
It has been found that the anti-reflective coatings of the present invention exhibit high performance in photolithography processes for forming ultrafine-patterns using 193 nm ArF radiation. The same was also true of where 248 nm KrF, 157 nm F2 laser, E-beams, EUV (extremely ultraviolet) and ion beams are used as light sources.
The following examples are set forth to illustrate more clearly the principles and practice of this invention to one skilled in the art. As such, they are not intended to limit the invention, but are illustrative of certain preferred embodiments.